The disposal of mercury contaminated waste water, generated during the cleansing of contaminated glassware and as a result of analytical mercury testing procedures in conjunction with the use of organic mercurial agents to produce bacteriostatic water (phenyl mercuric nitrate) or preserve certain biological vaccines (thimerosal), poses a major problem in the pharmaceutical industry where relatively large volumes of water containing small amounts of both organic and inorganic mercury compounds are produced. Discharge waters to natural water bodies or directly to water treatment facilities may be required to contain undetectable mercury concentration to meet current environmental regulations. Present analytical methods are capable of detecting mercury in waste water in amounts as low as 0.2 parts per billion. Hence, very efficient water treatment processes are needed to obtain waste water purity levels meeting that restriction, without markedly increasing the cost of the vaccine which would require price increases in excess of consumer's price index guidelines.
U.S. Pat. No. 5,154,833 discloses a process for removing thimerosal from the effluent of a vaccine manufacture operation, to achieve what was then an environmentally acceptable level at less than 3 parts per billion mercury. The process involved (1) chlorinating the organic mercury compound (preferably with sodium hypochlorite) at a pH less than 3, to obtain a mercurous (H.sup.+) salt ion. (2) The aqueous solution was then dechlorinated in a three step operation involving (a) aeration for from 8 to 20 hours, preferably 12 to 20 hours to strip all gaseous chlorine from the solution, (b) addition of a stoichometric amount of sodium metabisulfite to tie up the rest of the hypochlorite (this requires analysis of the solution to determine how much hypochlorite is left after air stripping), and (c) treatment of the bisulfite containing solution with activated carbon to remove the sodium bisulfite bound hypochlorite, and (3) as the final step, passing the chlorine free solution over an ion exchange resin having thiol functional groups to covalently bond the mercury to sulfur.